UK light heavyweight Joshua Buatsi earned a win yet disappointing beginning to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close ten-round bout at the boxing arena.
But Parker found success, delivering effective individual punches in a fight where the approaches failed to mesh, with excessive holding marring the action.
Two judges had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They prevail," Buatsi stated in the arena as he was faced boos from the spectators.
The Londoner bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to earn a 20th pro success.
Some ringside observers felt the challenger, 31, merited the victory but the British boxer endured the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Slow Match
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers prepared to be aggressive in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to barely take the better rounds.
The audience's tolerance decreased because of frequent holding, with Parker slipping to the canvas various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Arthur beat Rea by split-decision in a terrific all-Manchester contest to win the continental championship.
The arena fell silent for a deeply poignant memorial before the fight as a bell ceremony tolled in honor of local hero Hatton, who succumbed at age 46 in recently.
It was the premier televised fight night in the location since the passing of Hatton. As the last bell ended, the stillness became a chant of "there's just one Ricky Hatton".
The fighting within the ring reflected the emotion. The eventual winner was floored by a significant blow squarely on the chin in the second round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red attire of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was marked up early, heavy swelling developing under his face as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over 12 rounds.
Arthur barely secured the decision with scoring tallies of draw, close margin and clearer margin, but the two athletes were persistent and courageous, exactly what their hero the legend represented.
